Prior to this invention, co-workers Fletcher, Wadsworth and Bender developed a class of dyes useful for, among other things, imaging elements and methods wherein a mono-halogenated compound is reacted with the oxidized form of the reaction product of a pyridine and a cyclopropenone. The oxidation of the reaction product in this development by Fletcher et al preferably features the use of oxygen from air. Although such dyes, imaging elements and methods are highly useful, it would be advantageous to develop a dye reaction that is independent of oxygen. In such a case imaging elements could be constructed with overcoats that provide a variety of functions without regard to whether the overcoats also are readily permeable to air or other sources of oxygen.
The above-noted development is described and claimed in commonly owned U.S. application Ser. Nos. 278,022 & 278,013, filed on June 29, 1981 & June 29, 1981 by Fletcher, Bender & Wadsworth, entitled "Oxo-Indolizine and Oxo-Indolizinium Dyes and Processes For Their Preparation" and "Photographic Materials and Processes Comprising Oxo-Indolizine and Oxo-Indolizinium Compounds".